Release agent composition for improved coefficient of friction

ABSTRACT

A functional amine release agent displaying reduced coefficient of friction as compared to standard silicone oils, comprises a polydimethylsiloxane oil and a functional amine selected from the group consisting of pendant propylamines and pendant N-(2-aminoethyl)-3-aminopropyl. The concentration of functional amine to polydimethylsiloxane oil is approximately less than 0.0001 meq/g. According to certain embodiments, the functional amine release agent is operable to impart a coefficient of friction of about 0.5 or more to the print media, resulting in improved finishing and converting equipment interaction. The release agent may have a viscosity of about 50 cSt.

BACKGROUND

Solid inkjet imaging systems generally use an electronic form of animage to distribute ink melted from a solid ink stick or pellet in amanner that reproduces the electronic image. In some solid inkjetimaging systems, the electronic image may be used to control theejection of ink directly onto a media sheet. In other solid inkjetimaging systems, the electronic image is used to operate printheads toeject ink onto an intermediate imaging member. A media sheet is thenbrought into contact with the intermediate imaging member in a nipformed between the intermediate member and a transfer roller. The heatand pressure in the nip help transfer the ink image from theintermediate imaging member to the media sheet, which is transportedfrom the system and deposited in a paper tray.

In solid ink imaging systems having intermediate imaging members, ink isloaded into the system in a solid form, either as pellets or as inksticks, and transported through a feed chute by a feed mechanism fordelivery to a melting device. The melting device heats the solid ink toits melting temperature and the liquid ink is delivered to a printheadfor jetting onto an intermediate imaging member. In the print head, theliquid ink is typically maintained at a temperature that enables the inkto be ejected by the printing elements in the print head, but thatpreserves sufficient tackiness for the ink to adhere to the intermediateimaging member. In some cases, however, the tackiness of the liquid inkmay cause a portion of the ink to remain on the intermediate imagingmember after the image is transferred onto the media sheet and theresidual ink may later degrade other ink images formed on theintermediate imaging member.

In continuous-web, direct-to-media printing, a fixing assembly is usedafter the ink is ejected onto the print media or web to fix the ink tothe web. The fixing assembly used depends on the type of ink. Forexample, when using melted phase change ink to form images, the fixingassembly may include a pair of rollers that defines a nip for applyingpressure to the ink and web to spread the ink on the web as the webpasses through the nip, as depicted in FIG. 5. The function of the pairof rollers, also referred to herein as a spreader, is to transform apattern of ink drops deposited onto a web by flattening and spreadingthe ink drops to make a more uniform and continuous layer. The spreaderuses pressure and heat to reduce the height of the ink droplets and fillthe spaces between adjacent drops.

One difficulty faced in the operation of the spreader is providing theweb and the ink deposited on the web to the spreader at a temperaturethat enables the ink deposited on the web to be spread uniformly forhigh image quality. Due to very fast processing speeds at which somecontinuous feed imaging devices operate, the ink deposited on the web atthe print station may be above a suitable temperature range as the imagepasses through the nip. This high ink temperature results in the inkbleeding into the web and possibly showing through to the opposite sideof the media web. Conversely, if the ink cools below the suitabletemperature range prior to reaching the spreader, the ink may not bemalleable enough to allow for sufficient line spread or adherence to theweb. In addition, the ink ejected by the printheads is generally muchhotter than the print medium, and, consequently, areas imaged with highink coverage may exit from the print zone at higher temperatures thanthe areas of the media web where little or no ink was ejected. Ink thatenters the spreader at varying temperatures can cause inconsistent andnon-uniform line spread on the web, reducing image quality. Thus,improved media and ink temperature equalization is desirable. Foroptimum spreader performance, ink and web temperatures are substantiallyequalized prior to entering the nip to within a target temperature rangethat promotes adherence of the melted ink to the web, minimizesvisibility of printed ink from the opposite side of the media(“show-through”), maximizes ink dot spread, and reduces image defects onthe opposite side of the media in a duplex printing process. The targettemperature range for the ink and web prior to entering the nip can alsobe referred to as the pre-spreading temperature range. In oneembodiment, the pre-spreading temperature range is between about 50° C.and about 55° C. The pre-spreading temperature range, however, can beany suitable range of temperatures suitable for spreading ink on a webdepending on factors such as the ink formulation, web substratematerial, web velocity, and the like.

To address and/or prevent the accumulation of ink on an intermediateimaging member or on a spreader, which may be in the form of a drum,solid ink imaging systems may be provided with a drum maintenance unit(DMU), as shown in FIG. 5, that releases an oil or an oil blend thatlubricates the image receiving surface of the intermediate imagingmember before each print cycle, thereby preventing ink offset to thespreader drum. Typically, these DMU oils are silicone oils that maycontain additives to allow for proper lubrication and releasecharacteristics.

However, use of known DMU oils often results in imparting a coefficientof friction to the media being printed that is significantly lower thanthat of the native media. As such, the printed media is more slipperythan native media, which can interfere with many downstream productionfinishing or converting equipment that is used, for example, to handle,cut, fold, insert (as in mail-envelope inserters) or collate the printedmaterial leaving the print engine. Specifically, production finishing orconverting equipment is typically calibrated to handle media having thecoefficient of friction similar to native paper. Therefore, impartingprinted media with a lower coefficient of friction through the use ofDMU oils often results in feeding failures and/or production failureswith production finishing or converting equipment.

As such, a DMU oil formulation for use in solid ink jet color web-pressprinters is desirable that provides sufficient lubrication to an imagereceiving surface of the intermediate imaging member and image fixingmembers (i.e. a spreader drum) without imparting a coefficient offriction to the printed media that interferes with production finishingor converting equipment.

SUMMARY

According to certain embodiments, the present application relates to afunctional amine release agent comprising: a polydimethylsiloxane oiland a functional amine selected from the group consisting of pendantpropylamines and pendant N-(2-aminoethyl)-3-aminopropyl whereby theratio of functional amine to polydimethylsiloxane oil is approximately0.0001 meq/g. The release agent may have a viscosity of about 50 cSt.According to certain embodiments, the functional amine release agent isoperable to impart a coefficient of friction of not less than about 0.4to a print media when placed in contact with said media. In otheroptional embodiments, the functional amine release agent is operable toimpart a coefficient of friction of not less than about 0.5 to a printmedia when placed in contact with said media.

According to at least one embodiment, the present application relates tomethod for printing an image in a solid ink jet color web-press printer,comprising: providing an ink jet printer selected from the groupconsisting of: a solid ink jet color web-press printer having anintermediate imaging member and a solid ink jet color web-press thatprints using the direct-to-paper process; providing a functional aminerelease agent comprising a polydimethylsiloxane oil and a functionalamine selected from the group consisting of pendant propylamines andpendant N-(2-aminoethyl)-3-aminopropyl; and printing an image on a printmedia, whereby a resulting print surface has a coefficient of frictiongreater than about 0.3. In certain optional embodiments, theconcentration of functional amine to polydimethylsiloxane oil isapproximately 0.0001 meq/g.

According to one aspect, the printing process is performed using imagefixing members, such as a spreader drum and a pressure roll, and therelease agent of the present invention allows reduction of certain printprocess offset threshold temperatures for these components for simplexprinting. In one embodiment, the release agent disclosed herein permitsa reduction in the simplex offset threshold to a temperature that is 5°C. lower than the standard silicone DMU oil.

DESCRIPTION OF THE FIGURES

FIG. 1 is a graph of coefficient of friction as a function of aminepercentage in a release agent.

FIG. 2 is a graph of spreader drum offset level as a function oftemperature and release agent composition.

FIG. 3 is a graph of pressure roll offset level as a function oftemperature and release agent composition.

FIG. 4 is a graph showing a comparison of ink spreading as a function oftemperature.

FIG. 5 is a diagram of a fixing assembly in a print machine.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments described inthe following written specification. It is understood that no limitationto the scope of the invention is thereby intended. It is furtherunderstood that the present invention includes any alterations andmodifications to the illustrated embodiments and includes furtherapplications of the principles of the invention as would normally occurto one skilled in the art to which this invention pertains.

According to certain embodiments of the present application, a releaseagent composition for solid inkjet imaging systems is disclosed. Asdiscussed above, release agent compositions for solid inkjet imagingsystems are typically administered by an intermediate imaging member viaa delivery mechanism such as a drum maintenance unit (“DMU”) deliveryroll that may be at least partially immersed in a sump containing one ormore release agent compositions. In certain embodiments, a release agentcomposition of the present application is provided to the intermediateimaging member in an amount of from about 1 mg per sheet of blank A4sized paper to about 4 mg per sheet of blank A4 paper, and about 4 mgper sheet of blank A4 paper to about 10 mg per sheet of A4 paper for100% solid-fill. The system by which a release agent composition isprovided to an intermediate imaging member is well known, and may beaccomplished in a continuous or semi-continuous manner.

In certain embodiments, a release agent according to the presentinvention comprises a silicone oil and at least one functional aminegroup, resulting in a composition that does not impart a significantnegative reduction in the coefficient of friction to print media thatmight come in contact with the release agent. In particular, it has beenfound that utilizing a release agent which imparts a coefficient offriction of less than about 0.4, less than about 0.3, or less than about0.2 to the print media results in increasing degradation in performancein high speed production finishing and production equipment. As such,according to at least one exemplary embodiment, a release agentcomposition for solid inkjet imaging systems comprises approximately99.9999% by mole % non-functional silicone oil, and approximately0.0001% by mole % functional amine.

According to certain exemplary embodiments, a release agent comprises anamino functionalized polydimethylsiloxane release agent created byutilizing an amine-containing polydimethylsiloxane concentrate andsubsequently diluting with nonfunctional polyorganosiloxane oil toprovide a release agent with a relatively consistent distribution ofamines in a large volume of polydimethylsiloxane oil. In producing theamine-containing polydimethylsiloxane concentrate, an end blocker, aminosiloxane, catalyst and octamethyltetracyclosiloxane are reacted in avessel at elevated temperature (of from about 100 to about 210.degree.C., or from about 145 to about 185.degree. C.), for a desired time (offrom about 2 to about 15 hours, or from about 5 to about 10 hours). Theresulting reaction product is then diluted with non-functionalpolydimethylsiloxane for use as a release agent composition for solidinkjet imaging. In accordance with the present disclosure, the amountand concentration of the non-functional polydimethylsiloxane may beadjusted depending upon the initial coefficient of friction of the printmedia, but should result in a composition which does not impart acoefficient of friction (COF) that is less than about 0.4, andpreferably not less than about 0.5 to the paper or media being printedupon by the solid inkjet printer. It will be appreciated that blendingmay be performed according to blending techniques provided by WackerSilicones Corp. of Adrian Mich. According to other certain embodiments,the amount and concentration of the non-functional polydimethylsiloxanemay be adjusted depending upon the initial coefficient of friction ofthe print media, but should result in a composition which does notreduce the coefficient of friction to the paper or media being printedupon by the solid inkjet printer by more than about 0.2.

According to certain exemplary embodiments, suitable amino-functionalrelease agents include pendant propylamines and pendantN-(2-aminoethyl)-3-aminopropyl functional groups. For example, accordingto certain embodiments, a pendant propylamine release agent includethose having the following structure:

Further, according to certain embodiments, a pendantN-(2-aminoethyl)-3-aminopropyl release agent include those having thefollowing structure:

Alternatively, a blend of two amino-functional release agent materialscan be used as the release agent composition. For example, a blend oftwo or more of the above-described amino-functional release agents canbe used. In certain embodiments, the blend comprises two differentrelease agent materials of the above structures. In other embodiments, ablend of two or more different amino-functional release agents havingthe above amine concentrations can be used.

According to certain alternative embodiments, amine stabilizers areutilized, such as hindered amine light stabilizers including2,2,6,6-tetramethyl piperidine and its derivatives.

As can be seen by the following exemplary embodiments, the use ofamino-functional release agents according to the disclosure hereinresults in an increased coefficient of friction with respect to standardpolydimethylsiloxane oils.

Example 1

According to one exemplary embodiment, a pendantN-(2-aminoethyl)-3-aminopropyl release agent was created according tothe above system by adding an amine-containing polydimethylsiloxaneconcentrate and subsequently diluting with polydimethylsiloxane to aconcentration of approximately 0.0001 meq/g. Thereafter, the pendantN-(2-aminoethyl)-3-aminopropyl release agent was administered to a solidink jet color web-press printer, and the printer was used to processprint jobs as compared to a standard silicone oil. In this instance, thestandard silicone oil used was Copy-Aid 270; 72 cSt, 0.01 meq/gfunctional amine (available from Wacker Silicones; Adrian, Mich., USA).The graph of FIG. 1 shows a comparison of the COF for the release agentof the present invention (0.0001 meq/g) as compared to the COFs forvirgin substrate, the standard silicone oil (0.01 meq/g) and anintermediate release agent (0.0006 meq/g). This graph demonstrates thatthe release agent disclosed herein (0.0001 meq/g) results in a COF ofgreater than 0.4 and greater than 0.5, whereas the other release agentsproduces significantly lower COFs approaching half the COF of the virginsubstrate.

The above testing substantiates that the reduction in number of aminemolecules present on the substrate leads to a corresponding increase inCOF of the printed output. In accordance with the present invention, a100× reduction in amine molecules from the standard DMU release agent tothe 0.0001 meq/g value of the present disclosure can provide asignificant advantage over the prior release agents, particularly inconjunction with demanding finishing equipment requirements. However,the release agent of the present invention allows reduction of certainprint process offset threshold temperatures. FIG. 2 is a graph ofspreader drum offset levels as a function of spreader drum temperaturefor simplex printing. FIG. 3 is a similar graph for pressure roll offsetlevels in duplex printing. As reflected in FIG. 2, the lower meq/grelease agent drops the simplex offset threshold to 53° C. (at offsetlevel 1.0), which delivers a spreader drum recipe temperature of 48° C.that is 5° C. lower than the standard silicone DMU oil. FIG. 3 shows asimilar 5° C. decrease for duplex operation in which the pre-spread webtemperature is about 50° C. vs. the 55° C. temperature for the standardoil. It has been found in the testing that in the apex mode, the upperturn roll offset threshold is generally unchanged with the release agentof the present disclosure.

The graph of FIG. 4 illustrates the effect of the 5° C. decrease inthreshold temperatures. In particular, this graph shows that the reducedtemperature does not result in a significant decrease in the amount ofink spread (as measured by line width) delivered in the spreader system.In practical terms, use of the release agent of the present disclosurewill not negatively impact the image quality in any print mode

While the invention has been described in detail with reference tospecific and preferred embodiments, it will be appreciated that variousmodifications and variations will be apparent to one of ordinary skillin the art. All such modifications and embodiments as may readily occurto one skilled in the art are intended to be within the scope of theappended claims.

What is claimed is:
 1. A functional amine release agent comprising: apolydimethylsiloxane oil; and a functional amine selected from the groupconsisting of pendant propylamines and pendantN-(2-aminoethyl)-3-aminopropyl; whereby concentration of functionalamine to polydimethylsiloxane oil is less than 0.0001 meq/g.
 2. Thefunctional amine release agent of claim 1, wherein the functional aminerelease agent has a viscosity of 50 cSt.
 3. The functional amine releaseagent of claim 1, wherein the functional amine release agent is operableto impart a coefficient of friction of not less than 0.4 to a printmedia when placed in contact with said media.
 4. The functional aminerelease agent of claim 3, wherein the functional amine release agent isoperable to impart a coefficient of friction of not less than 0.5 to aprint media when placed in contact with said media.
 5. The functionalamine release agent of claim 3, wherein the print media is paper.
 6. Thefunctional amine release agent of claim 1, wherein the functional aminerelease agent is operable to reduce the coefficient of friction of printmedia when placed in contact with said media by no more than 0.3.
 7. Thefunctional amine release agent of claim 6, wherein the functional aminerelease agent is operable to reduce the coefficient of friction of printmedia when placed in contact with said media by no more than 0.2.